Effects of Steroid Therapy on Pancreatic Endocrine Function in IgG4-related AIP: Evaluation by Arginine Stimulation Test

IgG4-related diseases are fibroinflammatory disorders affecting multiple organs, with autoimmune pancreatitis (AIP) being a common manifestation. Steroid therapy is effective in inducing remission but has complex effects on glucose metabolism. Diabetes occurs in 40% to 80% of AIP patients, and steroids can worsen glucose tolerance, although some studies suggest they may improve pancreatic endocrine function. An 81-year-old man with elevated IgG4 levels and imaging findings consistent with AIP initially declined treatment. His condition worsened, leading to poor glycemic management and referral to our hospital. Imaging confirmed AIP and tests showed impaired insulin and glucagon secretion. He was diagnosed with pancreatic diabetes secondary to IgG4-related AIP. Initially, intensive insulin therapy was administered, but within 3 months, both insulin and glucagon secretion declined significantly in the arginine-stimulation test, necessitating steroid therapy with prednisolone (35 mg/day) for the AIP. The high dose of steroid treatment enhanced both insulin and glucagon secretion capacities but gradually declined with dose tapering. On the other hand, although steroid therapy poses a temporary risk of hyperglycemia, it likely prevented further deterioration of pancreatic endocrine function.